Staphylococcus aureus is a common community-acquired and nosocomial pathogen. Antimicrobial resistance is an important feature of this organism and resistance is often due to R-plasmids. Plasmid acquisition of S. aureus has traditionally been felt to be via transduction. Studies in this laboratory have recently pointed to a novel mechanism of plasmid acquisition by S. aureus. Conjugation with either Streptococci or S. epidermidis as donor has been observed. This project proposes an exploration of this transfer from two aspects. Using phenotypic resistance to select donors, intergeneric, interspecies, and intraspecies transfer to S. aureus will be examined using filtermembrane matings. A screening procedure for determination of plasmid content by agarose-gel electrophoresis will be develoed and used to examine donor and transrecipients from successful matings. Experiments to exclude transduction and transformation will be performed. A broad information base as to the presence of transferable plasmids will be developed from these studies, and correlated with epidemiologic and clinical data to explore the importance of conjugal elements in the evolution of resistant S. aureus. In addition, we propose more detailed examination of selected individual transferable plasmids. Host range, ability to mobilize other plasmids, and mobilization of chromosomal genes will be examined using mating procedures. Dye-bouyant centrifugation will be utilized to obtain purified plasmid DNA from selected isolates. Plasmids will be characterized by determination of molecular mass, restriction enzyme digestion, and relatedness to known and newly discovered conjugal elements in S. aureus using in vitro hybridization techniques. These studies will provide insight into the molecular basis of the transfer process.